SEARCHLIGHT, Nev.—Harry Reid is thankful he quit boxing years ago as a young man, since "I'm not sure all those blows I took to the head did me much good" (Tweet This).

But he's happy to keep delivering punches as he winds down his career as Senate Democratic leader.

He rips the Koch brothers and other high-dollar donors for tilting the political process in the wake of the Citizens United Supreme Court decision. He smacked Rush Limbaugh's credibility for the radio broadcaster's suggestion that Reid "may have been beaten up" instead of suffering injuries in an exercise accident. He continues to question why 2012 Republican presidential nominee Mitt Romney never released years of income tax returns.

He calls the global warming views of Senate colleague James Inhofe "ridiculous," and describes Senate Republican leader Mitch McConnell as "a lump of coal" for his views on energy and the environment. Asked to assess prospects for the 2016 Republican presidential field, Reid responded: "I don't really care. I think they're all losers."

Reid's free-swinging style, employed on behalf of President Barack Obama and fellow Democrats in recent years, is why Republicans have increasingly made him a political target. In the 2010 midterm elections, he survived a major Republican push to end his career.

The 75-year-old Nevada Democrat, now completing his fifth term, hailed the Congress during the first two years of Obama's administration as "the most productive in the history of the country."

"I worked hard for" Obama, Reid said. "What he has tried to do—Wall Street reform, Obamacare, tobacco regulation, credit card regulation, all these things that have been so good for the country—I agree with."

Since the GOP regained control of the House in 2010, he added, Republicans have been determined to shut down Obama's agenda in a way unprecedented in recent history. "The job of every opposition is to do things that push back at the president in power, but not oppose everything," Reid said. He not only defended Obama for responding with executive action on issues such as immigration, but asserted, "I think he should have done it sooner."

Reid declined to back off his past criticism of then-Federal Reserve Chairman Alan Greenspan as a "political hack," citing Greenspan's willingness to say "whatever the president wants him to say." Asked if former Fed Chair Ben Bernanke had done the same thing under Obama, Reid noted that he'd been appointed by Republican President George W. Bush. He said Bernanke's successor, Janet Yellen, "has done well so far."

Joshua Roberts | Reuters

Sen. Harry Reid, D-Nevada, speaks during a press conference on Capitol Hill on March 17, 2015.

Reid praised the sharp increase in the number of women in the Senate for improving the chamber. He pronounced himself comfortable with Hillary Clinton as the party's 2016 presidential candidate, and isn't eager for her to face stiff competition.

"I am not a big fan of primaries," he said. "I don't think they help, especially when you're someone as noted as Hillary."

Asked if he would advise Vice President Joe Biden to skip the 2016 race, he responded: "He can make that decision on his own, without my advice."

Reid predicted that Democrats would hold his seat in 2016, when the presidential race is expected to swell turnout of Democratic-leaning constituents such as Latinos. He called his party's chance of regaining control of the Senate overall "far better than 50-50."

Reid is approaching his Senate retirement with significant health challenges. The exercise accident has cost him the sight in his right eye. As he recovers from post-accident surgery, doctors have scaled back his ability to exercise. He's largely limited to walking for now.

"I don't know what I'm going to do," Reid said. "I'm not going to lobby. I'm not going to practice law. But I'll keep busy. I may want one of your jobs—to be an analyst on TV—and say all these good things that you always say about me."